Aliens keep wiping themselves out before humans discover them.
Aliens wipe themselves out before humans can discover them
NASA scientists think that extraterrestrials could have existed throughout the history of the universe but have never survived long enough to make contact with Earth.
Boffins suggest that some of the aliens will have been wiped out by uncontrollable events such as an asteroid hitting a planet but others may have been self-inflicted by factors such as climate change.
The study says: "Evidence of life should exist in abundance on our galaxy alone.
"And yet in practice we've produced no clear affirmation of anything beyond our own planet.
"So, where is everybody?
"The silence of the universe beyond Earth reveals a pattern of both human limitation and steadfast curiosity."
The NASA experts issued a warning that "existential disaster may lay in wait" as society advances towards space exploration and ramps up the hunt for alien life.